There is often a need to determine the conditions at which certain mixtures of fluids, more specifically, gases, become flammable for the purposes of process design and/or safety development. Depending upon the application, it may be desirable to have a mixture of gases be flammable, or alternatively, it may be desirable to have a mixture of gases not be flammable. Thus, depending upon certain baseline conditions, such as temperature, pressure, or percent concentration, it is desirable to discover how certain combinations of conditions affects whether the mixture of gases is flammable or not. FIGS. 1A, 1B are illustrative examples of how the flammability of a gas mixture, for example, a fuel gas, oxygen, and an inert gas, changes depending upon the baseline conditions involved. In FIG. 1A, the baseline conditions are a pressure of 100 psig and a temperature of 100° C. In FIG. 1B, the baseline conditions are a pressure of 400 psig and a temperature of 100° C.
The data points in FIGS. 1A and 1B are obtained using a test apparatus that determines whether the gas mixture is flammable. The test apparatus is typically a spherical chamber into which the gas mixture is introduced. The spherical shape of the chamber maximizes the gas pressure that can be introduced into the chamber. A spherical chamber also allows for easier mixing of the gas within the chamber because a sphere does not contain any “dead zones” in which the gas can be trapped. However, a spherical chamber is expensive to manufacture, and the relative height to width of the spherical chamber may produce stratification within the chamber such that the composition of the gas mixture varies in a vertical direction. The expense of the spherical chamber is magnified because the spherical chamber must have a design burst pressure that exceeds the pressure in the chamber after the gases have been ignited. As a rule of thumb, the pressure in the chamber after the gases have been ignited is approximately eight times the pressure of the gases before ignition.
There is, therefore, a need for an improved test apparatus that is less expensive to manufacture but still provides good gas distribution throughout the chamber. Furthermore, there is a need to eliminate the necessity to form a chamber whose burst pressure is at least eight times greater than the highest initial pressure of gases being tested within the chamber. Still further, there is a need for a test apparatus that reduces stratification of gases within the test chamber.